The present invention relates to a zoom lens system for use in a photographic camera. More particularly, the present invention relates to a zoom lens system that is compact, has coverage varying from a wide angle end to a telephoto end and which yet achieves a high zoom ratio of from about 3 to 4. Also, the present invention relates to a macro-mode zoom lens.
A zoo lens system that has a zoom ratio of at least about 3 and which has coverage varying to a narrow-angle telephoto end cannot be effectively composed of a retrofocus type consisting of a negative first lens group and a positive second lens group (this is generally referred to as the "two-group" type) or a modified type wherein the second lens group is further divided into a positive, a negative and a positive lens unit. The reason for this inability is that the diameter of the second lens group and the amount by which it has to be moved are increased considerably.
Therefore, various other zooming methods have been proposed in published patent literature for constructing zoom lens systems of the class described above, and they include:
(1) an old "four-group" type which as shown in accompanying FIG. 2, consists of a positive focusing section (first lens group) that remains fixed during zooming, a negative and movable variator section (second lens group), a negative or positive compensator section (third lens group) and a positive fixed relay lens section (fourth lens group);
(2) a modification of the first type in which the first and fourth lens groups conventionally fixed are rendered movable and which therefore consists of a positive first lens group, a negative second lens group, a positive third lens group and a positive fourth lens group, all being movable (in some versions, the second lens group is fixed);
(3) a modification, not of the first type, but rather of the fourth type to be described just below, which includes a negative fourth lens group behind the a three-group type system in such a way that it is fixed or adapted to be movable to cause a monotonic increase (sometimes monotonic decrease) in the distance between the third and fourth lens groups (see FIG. 4);
(4) a system in which all of the three lens groups, i.e., a positive first lens group, a negative second lens group and a positive third lens group, are adapted to be movable (see FIG. 5);
(5) a modification of the fourth type in which the third lens group is composed of a positive lens unit 3a and another positive lens unit 3b, which are slightly adjustable in their distance (see FIG. 6(a), or which is further modified in such a way that lens unit 3a is composed of a single-element positive fixed lens component 3a' and a positive lens component 3a" [see FIG. 6(b)]; and
(6) a system which, as shown in FIGS. 7(a) and (b), is composed of a positive first lens group, a negative second lens group, a positive third lens group, a negative fourth lens group and a positive fifth lens group, all of these five lens groups being adapted to be movable (in some versions, either the second or fifth lens groups or both are fixed).
However, these systems have their own problems as described below.